History and exam

Key diagnostic factors

common

cough

An early symptom that typically increases in severity over several days. The quality of the cough can be variable, from dry to wet to croupy.[46]

tachypnea

May be seen in more severely affected infants. A very high respiratory rate is one risk factor for apnea.[2]

wheezing

Because the airways are obstructed by mucus and necrotic debris, wheezing and crackles are common symptoms.[46] However, some infants may be so severely obstructed or unable to generate high enough expiratory flow rates that audible wheezing is absent.

retractions, grunting, and nasal flaring

The pathologic effects of the infection may result in symptoms of increased work of breathing.[43]

Other diagnostic factors

common

rhinitis

This and other symptoms of an upper respiratory tract infection usually precede bronchiolitis by several days.[43]

fluctuating clinical findings

A hallmark of bronchiolitis, often occurring within short time periods.[47]

irritability, malaise, and poor feeding

Additional systemic signs can occur in bronchiolitis, such as irritability, malaise, and poor feeding.

fever <104°F (<40°C)

Most cases are associated with fever during the first few days of the illness. Fever is usually low grade and may no longer be present at the time of hospitalization.[46][61]

crackles

Physical exam usually reveals crackles, although not all infants present with this physical finding, and some clinical guidelines do not require crackles to be present to make the diagnosis.[43]

uncommon

apnea

Apnea can be due to respiratory muscle fatigue that occurs after hours of labored breathing, but more commonly it is of sudden onset at the beginning of the illness. It is not obstructive; the mechanism is unknown. It may be the sole presenting sign in infants, and some studies demonstrate that apnea occurs in up to 20% of hospitalized infants.[1]

Risk factors for apnea include age <1 month in full-term infants or <8 weeks' postpartum age for preterm infants, lower birth weight, very high or very low respiratory rates, and the presence of any previous apneic event at presentation to the hospital.[1][2]

thoracoabdominal asynchrony

This is the nonparallel motion of the ribcage and abdomen during inspiration, and can be seen in infants with airway obstruction due to bronchiolitis.[62]

Risk factors

strong

infants <3 years

The infection primarily affects infants (<3 years of age), with the peak incidence occurring between 2 to 6 months of age.

winter months

There is a distinct seasonal pattern that mirrors that of respiratory syncytial virus (RSV), the most common etiologic agent. The season in the northern hemisphere typically starts in early November, peaks in January or February, and is complete by April.[7] In the southern hemisphere, seasonal outbreaks occur from May through September.[7]

In countries closer to the equator where the weather is tropical, disease is more common during the rainy season.[33]

prematurity or bronchopulmonary dysplasia

Preterm birth is a well-recognized risk factor for more severe bronchiolitis.[34]

Preterm infants with chronic lung disease (also known as bronchopulmonary dysplasia) are at even greater risk for severe bronchiolitis. The factors that contribute to the severity of this condition in preterm infants include smaller airway caliber and reduced passive immunity from maternal immunoglobulin.[35] Infants with bronchopulmonary dysplasia have fewer alveolar airway attachments, contributing to increased airway obstruction during bronchiolitis.[36] Bronchopulmonary dysplasia can also be associated with mucous gland hyperplasia, smooth muscle hypertrophy, and squamous epithelial cell metaplasia, all of which contribute to the severity of this infection.

passive tobacco smoke exposure and air pollution

Maternal smoking during pregnancy results in diminished airflow at birth, and continued environmental tobacco smoke exposure is associated with more severe bronchiolitis with increased risk of hospitalization.[19][20][21] Environmental tobacco smoke affects mucociliary clearance and bronchial hyperresponsiveness, both of which contribute to more severe disease.

Exposure to other sources of air pollution is associated with increased respiratory symptoms in infants and children, especially those with underlying lung disease.[37] Increased levels of 10-micron airborne particulate matter (PM10) have been associated with higher rates of RSV hospitalization in infants.[22]

impaired airway clearance and function

Cystic fibrosis is clearly associated with increased risk of severe bronchiolitis, but chronic aspiration, impaired airway clearance due to neuromuscular disease, and tracheomalacia have also been reported to be risk factors for more severe bronchiolitis.[38][39]

Premorbid lung function can affect the incidence of lower respiratory tract disease with viral respiratory infections.

congenital heart disease

Hemodynamically significant congenital heart disease is associated with more severe bronchiolitis, and the presence of pulmonary hypertension increases the risk of mortality.[40][41] Cardiac surgery performed in the presence of respiratory syncytial virus infection is also associated with increased mortality.

immunodeficiency

Children with primary or secondary immunodeficiency are at risk for severe disease as a result of respiratory syncytial virus (RSV) infection and may have protracted viral shedding. In this population, RSV-associated lower respiratory disease can also be seen in older children. Immunocompromised children are at risk for nosocomially acquired RSV infection.[42]

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